Distinguish between empty and absent tag values in
ContentDescriptionObjects. #29

mid3iconv:

Fix a crash when processing empty (invalid) text frames.

MAJOR API INCOMPATIBILITY!!!!

EasyID3FileType is now in mutagen.easyid3, not mutagen.id3. This
change was necessary to restore API compatibility with 1.16, as
1.17 accidentally contained a circular import preventing
mutagen.easyid3 from importing by itself. #32